Oracle MySQL 5.1 before 5.1.49 and 5.0 before 5.0.92 allows remote authenticated users to cause a denial of service (mysqld daemon crash) by using EXPLAIN with crafted "SELECT ... UNION ... ORDER BY (SELECT ... WHERE ...)" statements, which triggers a NULL pointer dereference in the Item_singlerow_subselect::store function.

storage/innobase/dict/dict0crea.c in mysqld in Oracle MySQL 5.1 before 5.1.49 allows remote authenticated users to cause a denial of service (assertion failure) by modifying the (1) innodb_file_format or (2) innodb_file_per_table configuration parameters for the InnoDB storage engine, then executing a DDL statement.

Oracle MySQL 5.1 before 5.1.49 allows remote authenticated users to cause a denial of service (crash) via (1) IN or (2) CASE operations with NULL arguments that are explicitly specified or indirectly provided by the WITH ROLLUP modifier.

Oracle MySQL 5.1 before 5.1.49 and 5.5 before 5.5.5 allows remote authenticated users to cause a denial of service (mysqld daemon crash) by using the HANDLER interface and performing "alternate reads from two indexes on a table," which triggers an assertion failure.